A pipe layer is a work vehicle used for installing pipes at petroleum and natural gas delivery pipeline construction sites and the like. For example, at a pipeline construction site, multiple pipe layers are lined up in a row and the pipe layers wind up a wire using a winch to lift up the pipes. The winch is coupled with a hydraulic motor and rotated by hydraulic pressure.
A warm-up is performed to raise the temperature of the hydraulic fluid in typical hydraulic driven machines such as hydraulic excavators and the like. The warm-up generates a pressure loss to cause the hydraulic fluid temperature to be raised by causing the hydraulic fluid to pass through a throttle provided in a hydraulic circuit. Alternatively, the hydraulic fluid temperature may be raised by causing the hydraulic fluid to pass through a narrowed control valve in which the opening area is reduced.
For example, the hydraulic drive device described in Japanese Examined Patent Application Publication No. H2-35164 includes a directional switching valve. The directional switching valve adjusts the flow rate of hydraulic fluid supplied to a hydraulic cylinder. Then, when the opening area of the directional switching valve is reduced by narrowing, the temperature of the hydraulic fluid rises. Additionally, the hydraulic drive device includes an electromagnetic proportional control valve for controlling the opening area of the directional switching valve, and a control circuit that outputs control signals to the electromagnetic proportional control valve. The control circuit finely controls the opening area of the directional switching valve by optimally controlling the electromagnetic proportional control valve on the basis of a detected temperature of the hydraulic fluid.
Further, a hydraulic drive machine described in Japanese Patent No. 2715180 causes the hydraulic fluid temperature to be raised by reducing an opening area of a variable orifice by narrowing. The variable orifice has a solenoid and the opening area is changed in response to a signal input to the solenoid from a controller. The controller controls the variable orifice on the basis of information such as the displacement of an electrically operated lever, the rotational speed of the engine, or the hydraulic fluid temperature and the like.